Membership in Namco Bandai's social One Piece game One Piece Grand Collection has topped the million mark, the publisher announced today.

While three other Namco Bandai social games have topped the million user mark, One Piece managed the feat just four days after it became available for play.

One Piece Grand Collection is available on the Mobage mobile social platform. Players collect figures of their favorite One Piece characters, and face off against rival boss characters in battle. As with all Mobage games, basic play is free.